Layered naturally occurring and synthetic smectites such as bentonite, montmorillonites and chlorites may be visualized as a sandwich comprising two outer layers of silcon tetrahedra and an inner layer of aluminum octahedra. These clays are generally representable by the general formula: EQU (Si.sub.8).sup.iv (Al.sub.4).sup.vi O.sub.20 (OH).sub.4
where the iv designation indicates an ion coordinated to four other ions, and the vi designates an ion coordinated to six other ions. The iv coordinated ion is commonly Si.sup.4+, Al.sup.3+, or Fe.sup.3+, but could also include several other four-coordinate ions, e.g., p.sup.5+, B.sup.3+, Ga.sup.3+, Cr.sup.3+, Ge.sup.4+, Be.sup.2+, etc. The vi coordinated ion is typically Al.sup.3+ or Mg.sup.2+, but could also include many other possible hexacoordinate ions, e.g., Fe.sup.3+, Fe.sup.2+, Ni.sup.2+, Co.sup.2+, Li.sup.+, Cr.sup.3+, V.sup.2+, etc. The charge deficiencies created by substitutions into these cation positions are balanced by one or more cations located between the structure's platelets. Water may be occluded between the layers and either bonded to the structure itself or to the cations as a hydration shell. Commercially available clays of this type include the above mentioned montmorillonite, bentonite, hectorite, beidellite, nontronite, and a host of other smectite materials from hundreds of localities, often having local names and specific compositions.
Normally the clay structure yields repeating plate every 9 .ANG. or thereabouts. Much work has been done to demonstrate that these platelets may be separated further, i.e., interlayered, by insertion of various polar molecules such as water, ethylene glycol, various amines, etc., and that the platelets can be separated by as much as 30 to 40 .ANG..
Some prior workers have prepared phosphated interlayered clays for use as low temperature traps for slow release fertilizers.
U.S. Pat. Nos. 3,803,026; 3,844,979; 3,887,454; and 3,892,655 describe layered clay-like materials and the process for using these materials. The layered materials are prepared from synthetic solutions of silica, alumina and magnesia salts. The final product has non-exchangeable alumina between the layers and an interlayer spacing greater than about 6 .ANG.. Such a spacing is characteristic of an anhydrous product.
U.S Pat. No. 3,275,757 also discloses synthetic layered type silicate materials as does U.S. Pat. No. 3,252,889. U.S. Pat. No. 3,586,478 discloses a method of producing synthetic swelling clays of the hectorite type by forming an aqueous slurry from a water soluble magnesium salt, sodium silicate, sodium carbonate, or sodium hydroxide and materials containing lithium and fluoride ions. The slurry is hydrothermally treated to crystallize a synthetic clay-like material.
U.S. Pat. Nos. 3,666,407 and 3,671,190 describe other methods of preparing clay-like materials. All of these synthetic clays are acceptable raw materials for use in the instant invention in place of naturally occurring clays. However, by virtue of the ready availability of large quantities of the natural clays at low prices, natural clays will generally be used in the practice of the present invention.
U.S. Pat. Nos. 3,798,177 and 4,060,480 disclose the preparation of hydroxy- aluminum modified smectite clays wherein a gibbsite-like layer is formed between the crystalline layers of the clay. The gibbsite-like layer is characterized by 14 .ANG. spacing, is continuous and does not substantially increase the internal pore volume of the modified clay material.
U.S. Pat. No. 4,060,480 discloses a process for the preparation of a crystalline catalyst support via the steps of treating montmorillonite clay with a hydroxy-aluminum solution. Clay, after contact with such solution, flucculation, removal from the solution by filtration, is then suspended in fresh water and allowed to age. The aged hydroxy-aluminum treated clay slurry is refiltered and impregnated with catalytic materials such as palladium or other metals.
U.S. Pat. Nos. 4,176,090; 4,248,739; and 4,271,043 all discuss pillared interlayered clays which are prepared by reacting smectite clays with high molecular weight cationic metal complexes containing metals such as aluminum, zirconium, titanium and various alkaline earth metals. The high molecular weight complexes are prepared by hydrolysis or copolymerization of a metal complex such as aluminum chlorohydrol.
U.S. Pat. No. 4,216,188 teaches the production of montmorillonites cross-linked with aluminum hydroxide or with chromium hydroxide and a process for the production of those clays by the interaction of a colloidal suspension of montmorillonite and a buffered and aged colloidal solution of the aluminum or chromium hydroxide.
U.S. Pat. No. 4,367,163 discloses a method for intercalating smectite clays with various ionic silicon complexes such as silicon (acetylacetonato) cation. The imbibed clays are then subjected to heating to form silica pillars between the various sheets of the clay. Similar iron complexes have been introduced into clays to yield expanded structures. See, Yamanaka et al, Materials Res. Bull., 19 (1984), p. 161.
U.S. Pat. No. 4,410,751 discloses the production of a smectite host material having zirconium oxide intercalated therebetween. The zirconium oxide is said to be in the form of pillars. Other smallspacing, metal intercalated clays have been described by Brindley et al, infra.
U.S. Pat. No. 4,452,910 discloses expanded layer smectite clay having a regular pore structure suitable for catalytic uses. The patent also discloses a process for preparing that expanded clay by treating a suspension of the clay with a chromiumoligomer solution and then subjecting the thus-treated clay to a stabilization heat treatment in an inert gas atmosphere.
The present invention is substantially different than each of the disclosures cited above in that it is concerned with a composition of matter having multimetallic pillars intercalated between layers of smectite clay. It is also concerned with a method for modifying smectite type materials in such a way as to produce a substantial micropore structure in the materials and yield novel catalytic and sorbent products having utility in the petroleum, chemical and related industries. The resulting properties may be viewed as being more characteristic of crystalline zeolites than of clays.